Hypothyroxinemia: a subclinical condition affecting neurodevelopment.

Hypothyroxinemia with low levels of circulating free thyroxine and normal levels of thyrotropin, which is usually caused by iodine deficiency, may affect pregnant women even in apparently iodine-sufficient areas, and it is debated whether it increases the risk of neurodevelopmental abnormalities in children born to them. Epidemiological observations indeed indicate that this is the case. Animal models show abnormal brain cortical cytoarchitecture in pups born to mildly hypothyroxinemic dams. In regions where the availability and use of iodized salt is inadequate (where <90% of households use iodized salt), the WHO and the International Council for Control of Iodine Deficiency Disorders (ICCIDD) recommend iodine supplementation so that the total iodine intake is 250 µg/day to prevent iodine deficiency during gestation and lactation.